170 



Colchicine 



methylene group of tlie alkaloid has been oxidized to carbonyl.22, 5o 

 Molecular rearrangement is almost connnonplace in colchicine's 

 chemistry. It is inherent in the changes, already described, by which 

 the 7-membered rings ot the alkaloid or its derivatives become con- 

 tracted to 6-membered rings. It is also encountered in formation of 

 the carbinol (().8) by the action of nitrous acid on colchinol methyl 



MeO 



MeO 



NHAc 



( XXIII ) 



NHAc 



CO2H 



ether and is again found in dehydration of this carbinol whereby 

 deaminocolchinol methyl ether (and its isomeride) is produced. Both 

 of these reactions are known to involve Demjanow-type rearrange- 

 ments (Cook, Jack, and Loudon"'^) and through them ring B, initially 

 7-membered. is contracted and re-ex|jandcd in successive steps. More- 

 over, colchicine itself is sensitive to ultraviolet light and is isomeri/ed 

 in aqueous solution by simlight. 1 hereby three isomerides, namely 

 U-, IS-, and y-liunicolchicine are formed (Grewe and Wulf;'''- Santavy^-^) 

 but their molecular structures remain undetermined. 



Synthesis — the ultimate challenge of a natural product to the 

 organic chemist — has still 10 be achieved for colchicine although, at 



